Detection of cylinder knock in internal combustion engines is known. For example, it is known that the amplitude and duration of engine vibration at certain frequencies can indicate the presence of cylinder knock. Accordingly, conventional knock detection approaches may measure radiation from the engine at certain calibrated frequencies, and diagnose knock from the duration and magnitude of such radiation. Spark timing adjustments are made in direction to reduce or eliminate the diagnosed knock. Such adjustments generally compromise other control goals, such as engine performance or fuel economy, and thus should be made with discretion. For example, such adjustments should only be made when truly needed to mitigate the well-known negative effects of knock. Accurate knock detection is therefore desirable to diagnose when spark timing adjustments are truly needed.
Conventional knock detection approaches that diagnose knock from simple frequency analysis are susceptible to noise at the frequencies of interest. In typical internal combustion engine applications, this noise may be caused from such periodic events as piston bore contact or valve seating contact. False knock detection may result from this susceptibility to noise, resulting in unnecessary and detrimental spark timing adjustment.
It has been proposed that a functional relationship exists between an engine's propensity for knock and certain engine operating conditions. An estimation of an engine's propensity to knock at its present operation level as indicated by sensed operating conditions can be used to characterize the degree of confidence in sensed vibration as indicating a knock condition and not simply a noise condition.
Comparison of sensed engine operating conditions to fixed thresholds has been proposed for estimation of engine knock propensity. A series of binary conclusions, based on whether the sensed condition falls above or below the magnitude of the corresponding fixed threshold, are used to estimate knock propensity. Such binary conclusions discard valuable information on the magnitudinal relationship between the sensed parameters and their fixed thresholds, reducing the accuracy of the estimation of knock propensity, and increasing the potential that ignition timing may be retarded unnecessarily, degrading engine performance.
A generally known development in control theory is fuzzy logic, in which the shortcomings associated with hard thresholds and binary conclusions are avoided and the entire knowledge rulebase is available for evaluation in the control.
Accordingly, it would be desirable to adapt an approach to estimation of engine knock propensity incorporating the benefits of fuzzy logic, for increased accuracy in the estimation.